Controlling polymer architectures : high-throughput experimentation, tailor-made macromolecules and glycopolymers via "click" reactions

In nature, complex three-dimensionally ordered macromolecular architectures, such as proteins and DNA, can be found which are dependent on a high level of structural control in order to perform their desired biological tasks. Such systems are up to now not accessible by synthetic methods; however, in the last decades tremendous progress was made in the development of advanced living and controlled polymerization techniques. Besides, several outstanding organic reactions have been discovered and perfectionated with their easy experimental conditions and resulting high yields, which are categorized as "click" reactions. These techniques allow researchers to prepare well–defined tailor–made macromolecules with before not accessible control. However, in particular living and controlled polymerization techniques require a delicate selection of the appropriate catalyst, initiator, and solvent at a certain polymerization temperature and period for each type of monomer. Therefore, high–throughput experimentation (HTE) tools and techniques are required to screen the effect of reaction parameters in relatively short times. These polymerization techniques and the application of HTE in polymer science have been reviewed in the first chapter. A major part of this thesis deal with the optimization of not only controlled radical polymerization techniques but also cationic ring opening polymerization (CROP) process. Nitroxide mediated radical polymerization (NMP) of several monomers have been performed in an automated parallel synthesizer to obtain the most optimum reaction conditions in means of polydispersity indices, number average molar masses, monomer conversions as well as block copolymerization. We have used for this purpose a unimolecular nitroxide initiator (ß-phosphonylated alkoxyamine, Bloc Builder) which has a relatively low decomposition temperature and provides good control over the polymerization progress. Some of the obtained polymer libraries were examined for their thermal properties and lower critical solution temperature behavior. The results of these experiments are discussed in detail in the second chapter. In the third chapter, we have focused on the reversible addition fragmentation chain transfer (RAFT) polymerization technique to synthesize methacrylic acid containing thermo-responsive copolymer libraries. These polymers have been prepared using a synthesis robot and also parallel characterization techniques were employed. Furthermore, water uptake properties of the hydrophilic polymers as well as thermo-responsive polymers have been investigated. It was demonstrated that responsive polymers behave hydrophilic below their LCST and hydrophobic above their LCST, thus exhibiting a reversible water uptake–release profile. Atom transfer radical polymerization (ATRP) is one of the most important controlled/"living" polymerization techniques which has attracted significant attention in many fields of chemistry. We have contributed for the further development by introducing a new tetradentate nitrogen based ligand for the ATRP of methyl methacrylate and styrene. The optimization results revealed that this ligand is suitable to conduct ATRP of methyl methacrylate (MMA) in the presence of Cu(I) and Cu(II) metal ions. Besides, this ligand has been used for the ATRP of styrene initiated from functionalized surfaces. Grafting from the surface resulted in the formation of polymer brushes with controlled lengths depending on the reaction time. Transformation of the polymerization mechanisms by post polymerization modifications or by using functional initiating/terminating agents have been of great interest to combine different classes of monomers on the same backbone. Therefore, we have employed for the first time a heterofunctional initiator for the ATRP of styrene and the CROP of 2-ethyl-2-oxazoline (EtOx) to synthesize amphiphilic block copolymers. Furthermore, we determined the optimum polymerization temperature for EtOx using acetyl halide type of initiators. These reactions have been performed systematically in a microwave synthesizer and the results have been discussed in the fifth chapter. "Click" reactions have been employed in many fields of chemistry since 2001. These efficient reactions attracted also polymer chemists to introduce functional end groups or side groups to well–defined polymers. Several different techniques have been published in the last eight years and we discussed critically the ones which do not require a metal catalyst during the reactions in the last chapter. Besides, we have introduced a metal-free "click" reaction between thiol and pentafluorophenyl groups to synthesize glycopolymers. For this purpose, fluorinated polymers have been prepared by NMP and were further functionalized using this new "click" chemistry route. In conclusion, this thesis provides new insights into the most important controlled radical polymerization techniques by utilizing in the automated parallel synthesis platforms and by the systematical preparation of copolymer libraries. The detailed characterization of these libraries provided fundamental knowledge on the structure-property relationships. Moreover, a new ligand for the ATRP of MMA and styrene, a new type of heterofunctional initiator for the combination of ATRP and CROP, and a new type of "click" reaction for the synthesis of glycopolymers have been introduced during this thesis. These new compounds and routes will be employed further for the preparation of tailor-made macromolecules to be used in specific applications

Scale-up of microwave-assisted polymerizations in continuous-flow mode : cationic ring-opening polymerization of 2-ethyl-2-oxazoline

Controlled radical polymerization (CRP) techniques are providing tremendous advantages for the synthesis of well-defined polymers with desired architectures. Nitroxide-mediated radical polymerization is one of the three most important CRP techniques and is used in industrial applications. In this study, two important parameters of the nitroxide-mediated radical polymerization technique were examined. Several polymerization temperatures (from 90 to 130 °C) and free nitroxide concentrations (from 0 to 10%) were investigated for the nitroxide-mediated radical polymerization of styrene and tert-butyl acrylate with MAMA as SG-1 based initiator. The optimization of those parameters was performed in a parallel manner on an automated synthesis platform

Lower critical solution temperature behavior of comb and graft shaped poly[oligo(2-ethyl-2-oxazoline)methacrylate]s

Comb and graft polymers with lower critical solution temperature (LCST) behavior based on hydrophilic oligo(2-ethyl-2-oxazoline) side chains and a hydrophobic methacrylate backbone were synthesized using the macromonomer method. Well-defined oligo(2-ethyl-2-oxazoline) methacrylate (OEtOxMA) macromono- mers were obtained by direct end-capping of living oligo(2-ethyl-2-oxazoline) chains with in situ formed triethylammonium methacrylate. The macromonomers were subsequently polymerized in a controlled manner using the reversible addition-fragmentation chain transfer (RAFT) polymerization technique yielding a series of comb polymers with varying side chain length and backbone length. In addition, a series of graft copolymers were prepared by copolymerizing OEtOxMA with methyl methacrylate (MMA, 40-80 mol %). The copolymers were characterized by 1H NMR spectroscopy, size exclusion chromatography (SEC), and, partially, by matrix- assisted laser desorption ionization (MALDI-TOF) mass spectrometry. The LCST behavior of aqueous polymer solutions was investigated by turbidity measurements revealing cloud points that can be tuned from 35 to 80 °C by variation of the MMA content. © 2009 American Chemical Society

Patterned polymer brushes grafted from bromine-functionalized, chemically active surface templates

Patterned polymer films are grafted from chem. active surface templates prepd. by the localized electrochem. oxidn. of an n-octadecyltrichlorosilane monolayer to form addressable areas for the site-selective binding of a bromine-terminated precursor. Atom-transfer radical polymn. of polystyrene generated stable, patterned polymer structures of different shapes and dimensions (see image). Electroprinting was used to generate features in the micro/mm range

High-throughput optimization of nitroxide mediated radical polymerizations as basis for the synthesis of temperature-responsive copolymers

The development of controlled radical polymn. techniques, namely atom transfer radical polymn. (ATRP), reversible addn. fragmentation transfer (RAFT) and nitroxide mediated radical polymn. (NMP), have opened up unprecedented possibilities for the synthesis of well-defined macromol. architectures with a large no. of different monomers. In addn., well-defined polymers with LCST behavior have wound widespread interest for a use as -smart' responsive materials. Here we report our automated parallel investigations on the NMP of 2 hydroxypropylacrylate (HPA), N,N-dimethylacrylamide (DMA) and N-acryloyl morpholine (Amor) using BlocBuilder- nitroxide and addnl. free SG-1 nitroxide. The high-throughput approach allowed fast optimization of the polymn. procedure for solvent, temp. and concn. of free nitroxide. In addn., the optimal polymn. conditions were applied for the synthesis of systematical libraries of well-defined statistical copolymers based on HPA and DMA or Amor. The effect of monomer compn. on the thermal properties and thermoresponsiveness of the copolymers was studied in detail. [on SciFinder (R)

Copolymers by radical polymerization containing phosphorescent iridium(III) complexes

No abstract

Scale-up of microwave-assisted polymerizations in continuous-flow mode : cationic ring-opening polymerization of 2-ethyl-2-oxazoline

Controlled radical polymerization (CRP) techniques are providing tremendous advantages for the synthesis of well-defined polymers with desired architectures. Nitroxide-mediated radical polymerization is one of the three most important CRP techniques and is used in industrial applications. In this study, two important parameters of the nitroxide-mediated radical polymerization technique were examined. Several polymerization temperatures (from 90 to 130 °C) and free nitroxide concentrations (from 0 to 10%) were investigated for the nitroxide-mediated radical polymerization of styrene and tert-butyl acrylate with MAMA as SG-1 based initiator. The optimization of those parameters was performed in a parallel manner on an automated synthesis platform

High-throughput investigations on the nitroxide mediated polymerization conditions using an automated parallel synthesizer

No abstract

MALDI-TOF MS/MS measurements of PMMA

The polymer poly(Me methacrylate) (PMMA) was analyzed using the matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) technique. The MALDI-TOF MS app. was coupled with a collision-induced dissocn. (CID) unit. The performance of the MALDI-TOF/TOF MS method in polymer anal. was demonstrated using a PMMA calibration std. The CID unit allowed the fragmentation of single peaks from the MALDI-TOF/TOF MS spectrum. The distributions obsd. in the 2nd level mass spectra depend on the end groups of the PMMA macromol. and on the fragmentation process. The MALDI-TOF MS/MS technique is suitable to det. the mol. compn., the end groups, and the sequence of a macromol. as well as the reaction mechanisms of polymn. reactions. [on SciFinder (R)